1. Field of the Invention
This invention generally relates to solid-state band-gap voltage reference circuits for providing an output voltage which is substantially constant with changes in temperature, and more specifically to an improved band-gap reference circuit in which temperature-compensation means operating at a constant current over the temperature range is provided to minimize changes in output voltage with changes in temperature. The invention also relates to improved circuitry for amplifiers having high gain characteristics.
2. Description of the Prior Art
In the past, Integrated Circuit (IC) band-gap reference circuits were constructed so as to pass unequal currents through a monolithically matched pair of transistor emitter-base junctions, or equal currents through unequal-area transistor emitter-base junctions, so as to obtain precisely defined differences in the characteristic band-gap voltages across the pair of junctions, and to derive therefrom a proportional voltage for use as a precision reference voltage. Such prior art, for example, is described in U.S. Pat. No. 3,617,859 (Dobkin, et. al. inventors) No. 3,887,863 (Brokaw inventor), and No. 4,250,445 (Brokaw inventor). The basic band-gap reference circuits of the prior art were relatively unsophisticated and large, complex, additional bias networks, current sources and loads were required in order for proper operation thereof.
Some of these prior-art circuits used passive loads and did not have sufficient open-loop voltage gain to provide a constant output voltage independent of temperature. These prior art circuits sometimes required cumbersome biasing circuitry. To use passive loads at low currents, resistors having large absolute values were required, thereby occupying unnecessarily large chip areas or semiconductor real estate. Because of relatively low loop gain in prior art band-gap voltage reference circuits, output voltage constancy as output load current varied (load rejection) was low.
Prior art band-gap voltage reference circuits generally employed a current through the band-gap transistor cell (or transistor pair) which was proportional to the ambient or semiconductor chip temperature.
A need existed for an improved band-gap voltage reference circuit in which the band-gap cell is biased at constant current throughout the temperature range, thereby improving temperature performance and saving power at high temperatures.
A need also existed for an improved band-gap voltage reference circuit whose complexity, device count and semiconductor area consumption for resistor devices would be low, so as to reduce the amount of semiconductor real estate or Integrated Circuit Chip area consumed.
A need further existed for an improved band-gap voltage reference circuit wherein the gain enclosed within a feedback loop was sufficiently high to improve constancy of output voltage despite variations in load current, supply voltage, ambient or chip temperature.
A need also existed for providing an improved amplifier having high gain characteristics and reduced device usage.